General Question

How does matter ever fall into a Black Hole?

As an object falls closer to the event horizon of a black hole time runs more slowly for that object as seen by an outside observer. As I understand it, the outside observer will see the object draw closer and closer but never quite reach the event horizon. That being the case how do black holes gather mass?

16 Answers

Time runs more slowly for the object as observed by an observer. It runs normally for the object falling in. The observer would see it slow down and then would see a 2 dimensional representation of the object right at the event horizon frozen just as it is falling in. If you are the object, however, you will be spaghettified and be sucked in.

All black hole information theoretical. The math involved to create these ideas also create puzzles. The end result is many different theories focused mainly on things that are hard to understand. The fact is that no one has ever encountered or studied a blackhole. The existence of blackholes is still up for debate.

@Rarebear I still don’t get it. An object falling into a black hole would not be aware of the event horizon. It would pass through the point of no return to its inevitable destruction at the singularity and so its mass would be added to that of the black hole.

But from the point of an outside observer, that is the rest of the universe, this doesn’t happen. For this observer the event horizon is a reality and as you say a falling object would appear to freeze upon its surface and never pass through. It seems to me that from the point of view of the rest of the Universe no objects can ever reach the singularity to add their mass to it.

I think it possible that all of the mass that a black hole accumulates exists only at the event horizon. An object entering the horizon is stretched about the entire event horizon, becoming part of the bubble surrounding the black hole. Any consciousness on board freezes as time becomes meaningless. The gravitational force of a black hole is generated in the event horizon. There is nothing inside but a hypothetical singularity. I know what I think may be foolishness.

@flutherother Yeah…you’re asking the right question. Not sure of the exact answer but I do know that when large amounts of mass are added, there are jets that will emit on the north and south poles of the black hole, and that gravity waves will propagate. I’ll check my sources and get back to you.

Bottom line is nobody really knows the answer to the question. But here are some answers that will not satisfy you, I don’t think. Matter doesn’t fall into a black hole directly, but rotates around it. That causes an accretion disk, that is visible. Also, because of the strong magnetic field from the rotating black hole and the accretion disc, there are jets that form on the poles of the black hole. In addition, gravity waves will be formed when matter falls in, and the event horizon radius increases.

@Bill1939 I think you may be right and from the point of view of an outside observer the falling object becomes smeared over the entire surface of the event horizon. What I don’t understand is that for the outside observer this should appear to take an infinite amount of time.

An observer falling into the black hole will experience things differently. He will be unaware of the event horizon and will instead fall into the singularity in a finite time, a very short space of time in fact.

At the event horizon, space and time are wrapped around and dragged by the spinning mass. Is the integrity of an object drawn into the horizon maintained while being distributed about the hole? The answer would be yes, if information is not to be lost.

The length of time it takes for our hypothetical object to go from the initial point of contact to becoming another layer of the event horizon would be long, as measured by our mythical outside observer, if only because of the area involved and not counting the effects temporal distortions. Maybe not infinite, just aeons.

I heard a lecture by Leonard Susskind that explains it after a fashion. He said that to an outside observer nothing will ever reach the event horizon as it takes an infinite amount of time. However as the object approaches the event horizon it bulges out to meet it. Ultimately the radius of the black hole is increased by absorbing the new mass. Effectively the infalling object never reaches the original event horizon as a new and larger one is created.

@flutherother, that is how I imagined it. One question is whether there is any inside to a black hole? My thought is dispite the volume enclosed by the event horizon, that the interior is a singularity (not just at the center of the black hole).

@Bill1939 I think that is right. In the same way an electron is both a particle and a wave Susskind says a black hole also has a dual nature and how it is seen depends on the observer. Someone falling into a black hole sees no event horizon and will pass through it oblivious to its existence. Nothing odd will be noticed.

For someone at a safe distance a singularity consists only of the event horizon and nothing else. There is nothing inside as everything the black hole contains is on the surface. There isn’t even space as all directions point the one way and space becomes like time. This can happen because although observers on either side of the event horizon experience totally different ‘realities’ they cannot communicate.

You can watch Susskind’s lecture here. He is a great lecturer and it is amazing that his talks are freely available on the web as he is one of the foremost thinkers in his field. The maths is utterly beyond me but I’ll take his word for it.